Molecular characterization of Hemimegalencephaly

体细胞突变，即体内部分细胞发生有害突变，在癌症中得到了很好的认识，但直到最近才在神经系统疾病中得到重视。在祖细胞群体中发生体细胞突变的情况下，所有子细胞都继承该突变，并能够作为分化程序的功能表达所产生的表型。我们最近在“半巨脑畸形”（HME）一种与大脑皮质发育畸形（MCD）相关的灾难性局灶性癫痫疾病中发现了首例发育中的大脑新生体细胞突变。HME是最严重的MCD综合征之一，其特征是两个大脑半球中任何一个的大量错构瘤过度生长。大脑半球切除术是一种常见的治疗顽固性癫痫，允许病变组织取样。通过将患病大脑的DNA与血液/唾液的DNA进行比较，我们发现了PIK3CA、AKT3或MTOR （MTOR通路的一部分）的新生体细胞突变。在手术中采集的不同脑区中，有8-40%的测序等位基因出现了突变，其中一些在已知的激活蛋白质的密码子中。然而，这项初步研究的样本量有限。本应用程序的目标是扩展我们的初步发现，并阐明HME的遗传，发育，信号和细胞生物学机制，特别是在哺乳动物皮层发育的背景下。我们将把HME患者患病脑的下一代测序与先进的生物信息学、完整的临床相关神经解剖学和小鼠模型相结合，以帮助我们进一步了解这一重要疾病的机制。我们将：1]在更大的回顾性和前瞻性收集的HME患者队列中检测新生体细胞突变。[2]将遗传疾病负担与临床、影像学和组织病理学结果（表型）联系起来。[3]测试这些新生突变如何改变发育中的大脑皮层祖细胞的功能。实验的目的是确定这些基因的突变是如何导致皮层发育中断的，为什么这些病变是癫痫性的，以及重新使用已批准的药物是否可能使患者受益，与其他局灶性发育不良和局灶性癫痫相关。

DESCRIPTION (provided by applicant): Molecular characterization of hemimegalencephaly Abstract Somatic mutations, in which a fraction of the cells in the body have a deleterious mutation, is well recognized in cancer but only recently appreciated in neurological disease. In the setting of a somatic mutation in a population of progenitor cells, all daughter cells inherit te mutation and are able to express the resultant phenotype as a function of the differentiation program. We recently identified the first de novo somatic mutations in the developing brain in the condition "hemimegalencephaly", (HME) a catastrophic focal epilepsy condition associated with a malformation of cerebral cortical development (MCD). HME is one of the most severe MCD syndromes, characterized by massive hamartomatous overgrowth of either of the two cerebral hemispheres. Cerebral hemispherectomy is a frequent treatment for the refractory epilepsy, allowing sampling of diseased tissue. By comparing DNA from diseased brain with DNA from blood/saliva, we identified de novo somatic mutations in PIK3CA, AKT3 or MTOR, part of the mTOR pathway. Mutations were present in 8-40% of sequenced alleles in various brain regions sampled during surgery, and some in codons known to activate the protein. However, the pilot study was based on a limited sample size. The goal of this application is to expand upon our initial findings, and elucidate the genetic, developmental, signaling and cell biological mechanisms of HME, particularly in the context of mammalian cortex development. We will combine next-generation sequencing of diseased brain from HME patients with advanced bioinformatics, complete clinical correlated neuroanatomy, and mouse modeling to help advance our understanding of the mechanism of this important disease. We will: 1] Test for de novo somatic mutations in a larger retrospectively and prospectively collected cohort of HME patients. 2] Correlate genetic disease burden with clinical, imaging, and histopathological findings (phenotype). 3] Test how these de novo mutations alter progenitor cell functions in the developing cerebral cortex. The goal of the experiments is to determine how mutations in these genes lead to disrupted cortical development, why these lesions are epileptogenic, and whether repurposing approved medications might benefit patients, with relevance to other focal dysplasias and focal epilepsies.